A family of nonimaging radiant energy direction devices has been developed and are described in the following references: U.S. Pat. Nos. 3,923,381, 4,002,499, 3,957,031, U.S. Pat. Ser. No. 850,340, U.S. patent application Ser. No. 714,863, and a publication, Applied Optics, Vol. 15, No. 2, Pages 291-292, Feb. 1976. Each of the devices referred to in these references was based on methods of design which utilized techniques of geometric optics, essentially the use of optical ray tracing together with experience about the behavior of reflectors of a variety shapes. The best known examples of this is the compound parabolic concentrator (CPC) described in U.S. Pat. No. 3,923,381.
When used as a second stage concentrator, CPC type devices have a practical disadvantage concerned with guidance of the concentrator system to face the sun. The entry aperture of the CPC is placed at the aberrated sun's image formed by the primary concentrator. Since the image will usually just fill the entry aperture, the system is very sensitive to guidance errors. Guidance errors of 0.1.degree. can cause losses as much as 20% of the flux. If a second stage with an entry aperture larger than the sun's image were used, some concentration is lost and the flux distribution over the exit aperture becomes nonuniform. Nonuniformity of flux distribution is very undesirable with photovoltaic cell arrays or heat absorbers. Thus the CPC type design prescription when applied to a second stage concentrator offers a good but not ideal solution.
There is herein disclosed a new class of nonimaging concentrators, some having maximumal theoretical concentration, not taught by the above described optical ray tracing methods. The method employs the geometrical vector flux quality of incoherent Lambertian radiant energy emitters. The overall design method can be shown to include those devices referred to in the above references as well as new devices which are particularly suited as second stage concentrators.
It is therefore an object of this invention to provide a radiant energy direction device.
Another object of this invention is to provide radiant energy concentration and collection devices particularly adaptable for the collection of solar energy.
Another object of this invention is to provide radiant energy concentrators particularly suited as second stage concentrators.